The present invention relates generally to zinc and magnesium-bearing aluminum alloys and processes for making the same. More specifically, the present invention is related to age-hardenable, high strength, high fracture toughness and high corrosion resistant aluminum alloys and processes of making the same.
Aluminum alloys have been used in the past in forming a variety of articles or products for structural applications. Some of those aluminum alloys are used in, for example, the aerospace industry. Designers and manufacturers in the aerospace industry are constantly trying to improve fuel efficiency and product performance. One method for improving such items is to produce lightweight materials with improved fracture toughness and corrosion resistance performance without losing relative strength.
The strengthening of age-hardenable aluminum alloys has traditionally involved solid solution heat treating, quenching, and natural or artificial aging. Natural aging generally consists of allowing the solution heat treated aluminum alloy articles to remain at about room temperature for a significant period of time. It is, however, commercially more feasible to artificially age these articles for shorter times at higher temperatures than room temperature. The strengthening of some aluminum alloys may include cold work, such as compression or stretching of the article: Cold work is typically performed on the age-hardenable aluminum alloy article before it is aged.
Accordingly, a need exists for a high strength, high fracture toughness and high corrosion resistant aluminum alloy and processes for making the same.
According to one process, an aluminum alloy is thermally treated. The aluminum alloy consists essentially of from about 5.7 to about 6.7 wt. % of zinc, less than 2.2 wt. % copper, less than 4.2 wt. % of the total weight percent of magnesium and copper combined, and less than 10.60 wt. % of the total weight percent of magnesium, copper and zinc combined, the balance being substantially aluminum, incidental elements and impurities. The article is solid solution heat treated and then quenched. The article is heated to a first temperature and artificially aged at the first temperature. The article is heated to a second temperature, wherein the second temperature is higher than the first temperature. The article is artificially aged at the second temperature of from about 290 to about 360xc2x0 F. for a duration of at least 6 hours. The article is cooled from the second temperature to 200xc2x0 F. at a cooling rate of from about 20 to about 40xc2x0 F./hour.
According to another process, an aluminum alloy is thermally treated. The aluminum alloy consists essentially of from about 5.7 to about 6.7 wt. % of zinc, less than 2.2 wt. % copper, less than 4.2 wt. % of the total weight percent of magnesium and copper combined, and less than 10.60 wt. % of the total weight percent of magnesium, copper and zinc combined, the balance being substantially aluminum, incidental elements and impurities. The article is artificially aged at a first temperature. The article is heated to a second temperature, wherein the second temperature is higher than the first temperature. The article is artificially aged at the second temperature of from about 290 to about 360xc2x0 F. for a duration of at least 6 hours. The article is cooled from the second temperature to 200xc2x0 F. at a cooling rate of from about 20 to about 40xc2x0 F./hour.
According to yet another process, an aluminum alloy is thermally treated. The aluminum alloy consists essentially of from about 5.7 to about 6.7 wt. % of zinc, less than 2.2 wt. % copper, less than 4.2 wt. % of the total weight percent of magnesium and copper combined, and less than 10.60 wt. % of the total weight percent of magnesium, copper and zinc combined, the balance being substantially aluminum, incidental elements and impurities. The article is artificially aged at a first temperature. The article is heated to a second temperature, wherein the second temperature is higher than the first temperature. The heat up rate from the first temperature to the second temperature is from about 25 to about 40xc2x0 F./hour. The article is artificially aged at the second temperature of from about 290 to about 360xc2x0 F. for a duration of at least 6 hours. The article is cooled from the second temperature to 200xc2x0 F. at a cooling rate of from about 20 to about 40xc2x0 F./hour.